Liquid-crystal polyester resin

ABSTRACT

The present invention provides a liquid-crystalline polyester resin, essentially consisting of the repeating units represented by formulae [I]-[IV]:  
                 
wherein p, q, r and s satisfy the following formulae: 0.4≦p/q≦2.0, 2≦r≦15, 2≦s≦15, and p+q+r+s=100, provided that the liquid-crystalline polyester resin has a melting point of 190-250° C. determined by differential scanning calorimetry. The liquid-crystalline polyester resin of the present invention exhibits a good molding processability at low temperatures and excellent mechanical properties.

TECHNICAL FIELD

The present invention relates to a wholly aromatic liquid-crystallinepolyester resin. More particularly, the present invention relates to awholly aromatic liquid-crystalline polyester resin which exhibits goodmolding processability at low temperatures and excellent mechanicalproperties.

BACKGROUND ART

Thermotropic liquid-crystalline polyester resin (which is called asliquid-crystalline polyester resin or LCP hereinafter) has goodproperties including heat resistance, mechanical properties such asrigidity, chemical resistance and dimensional accuracy and is used notonly for molded articles but also for a variety of products such asfibers and films. Particularly, personal computers and mobile phonesemploy highly integrated devices and the art wishes to use downsized,thinner and smaller parts for them. In the information andtelecommunication fields, very thin parts, as thin as 0.5 mm or less ofthe thickness, are sometimes required. Based on the excellent moldingproperties of the LCPs including good flowability and less flashdevelopment compared to the other thermoplastic resins, consumption ofthe LCPs has been increasing.

While the liquid-crystalline polyester resin exhibits high heatresistance, the LCP has extremely higher molding temperatures comparedto other engineering plastics such as polyethyleneterephthalate,polybutyleneterephthalate and polycarbonate. Accordingly, in someapplications, LCP may not be suitable because of its high moldingtemperatures.

The art desires the liquid-crystalline polyester resins which show thegood molding processability at low temperatures with retaining the goodmechanical properties, chemical resistance and dimensional accuracy ofwholly aromatic liquid-crystalline polyester resins. As an example ofliquid-crystalline polyester resins which exhibit good moldingprocessability at low temperatures, Patent literature 1 discloses aresin of which melting point determined by differential scanningcalorimetry is 270-280° C.

Patent literature 1: Japanese Patent Application Laid Open No. Sho.55-144024

DISCLOSURE OF THE INVENTION

Problems to be Solved by the Invention

An object of the present invention is to provide a wholly aromaticliquid-crystalline polyester resin which exhibits good moldingprocessability at low temperatures and excellent mechanical properties.

Means for Solving the Problems

The present invention provides a liquid-crystalline polyester resin,essentially consisting of the repeating units represented by formulae[I]-[IV]:

wherein Ar₁ and Ar₂ independently represent one or more bivalentaromatic group; p, q, r and s represent relative molar proportions (mol%) of the repeating units based on the total repeating units representedby formulae [I]-[IV] in the liquid-crystalline polyester resin andsatisfy the following formulae:0.4≦p/q≦2.0,2≦r≦15,2≦s≦15, andp+q+r+s=100,provided that the liquid-crystalline polyester resin has a melting pointof 190-250° C. determined by differential scanning calorimetry.

In the specification and claims, the term “liquid-crystalline polyesterresin” refers to a polyester resin which exhibits anisotropic melt phaseand is called as thermotropic liquid-crystalline polyester resin bythose skilled in the art.

The anisotropic melt phase can be confirmed by means of conventionalpolarized light system using orthogonal light polarizer. In more detail,the sample on the hot stage under nitrogen atmosphere may be observed.

In the specification and claims, p+q+r+s equals to 100 (mol %).

In the specification and claims, the term “essentially consisting of therepeating units represented by formulae [I]-[IV]” represents that theliquid-crystalline polyester resin of the present invention may compriseone or more additional resin component other than repeating unitsrepresented by formulae [I]-[IV] unless the additional resin componentdoes not impair the object of the present invention.

In other words, the liquid-crystalline polyester resin of the presentinvention may be prepared by copolymerizing the additional monomers withmajor monomers which provide the repeating units represented by formulae[I]-[IV].

Examples of such additional monomers include aromatic hydroxycarboxylicacid, aromatic diol, aromatic dicarboxylic acid, aromatichydroxydicarboxylic acid, aromatic hydroxyamine, aromatic diamine,aromatic aminocarboxylic acid, alicyclic dicarboxylic acid, aliphaticdiol, alicyclic diol, aromatic mercaptocarboxylic acid, aromaticdithiol, aromatic mercaptophenol and the like.

The proportion of these additional monomers to the total amount ofmonomers providing repeating units represented by formulae [I]-[IV] ispreferably no more than 10 mol %.

The liquid-crystalline polyester resin of the present inventionessentially comprises aromatic oxycarbonyl repeating units representedby formula [I] and formula [II] as repeating units:

wherein p and q represent molar proportions (mol %) of repeating unitsof formula [I] and formula [II] based on the total amount of repeatingunits of formulae [I]-[IV] in the liquid-crystalline polyester resin ofthe present invention.

According to the invention, the molar proportion between the repeatingunits of formula [I] and those of formula [II], i.e., p/q, is 0.4-2.0,preferably 0.6-1.8, and more preferably 0.8-1.6.

According to the invention, the molar proportions of each repeatingunits of formula [I] and formula [II] based on the total amount ofrepeating units of formulae [I]-[IV], i.e., p and q, are 35-48, andpreferably 38-43.

Examples of monomers which provide the repeating unit of formula [I] are6-hydroxy-2-naphthoic acid and ester forming derivatives such as acylderivative, ester derivatives and acyl halide thereof.

Examples of monomers which provide the repeating unit of formula [II]are p-hydroxybenzoic acid and ester forming derivatives such as acylderivative, ester derivatives and acyl halide thereof.

The liquid-crystalline polyester resin of the present inventionessentially comprises an aromatic dioxy repeating unit represented byformula [III] as a repeating unit:

wherein Ar₁ represents divalent aromatic group; r represents molarproportion (mol %) of the repeating unit of formula [III] based on thetotal amount of repeating units of formulae [I]-[IV] in theliquid-crystalline polyester resin of the present invention.

Preferably, the aromatic dioxy repeating unit represented by formula[III] is one or more moiety wherein Ar₁ is selected from the groupconsisting of:

Among the above, those wherein Ar₁ is:

are more preferable and that of which Ar₁ is:

is the most preferable.

Examples of monomers which provide the repeating unit of formula [III]are aromatic diols such as hydroquinone, resorcin,4,4′-dihydroxybiphenyl, 3,3′-dihydroxybiphenyl, 3,4′-dihydroxybiphenyl,4,4′-dihydroxybiphenylether, 2,6-dihydroxynaphthalene,2,7-dihydroxynaphthalene, 1,6-dihydroxynaphthalene,1,4-dihydroxynaphthalene and alkyl-, alkoxy- or halogen-substitutedderivatives thereof as well as ester forming derivatives such as acylderivative thereof.

The liquid-crystalline polyester resin of the present inventionessentially comprises an aromatic dicarbonyl repeating unit representedby formula [IV] as a repeating unit:

wherein Ar₂ represents divalent aromatic group; s represents molarproportion (mol %) of the repeating unit of formula [IV] based on thetotal amount of repeating units of formulae [I]-[IV] in theliquid-crystalline polyester resin of the present invention.

Preferably, the aromatic dicarbonyl repeating unit represented byformula [IV] is one or more of moiety of which Ar₂ is selected from thegroup consisting of:

Among the above, those wherein Ar₂ is:

are more preferable and that wherein Ar₂ is:

is the most preferable.

Examples of monomers which provide the repeating unit of formula [IV]are aromatic dicarboxylic acids such as terephthalic acid, isophthalicacid, 2,6-naphthalenedicarboxylic acid, 1,6-naphthalenedicarboxylicacid, 2,7-naphthalenedicarboxylic acid, 1,4-naphthalenedicarboxylicacid, 4,4 -dicarboxybiphenyl, bis(4-carboxyphenyl)ether and alkyl-,alkoxy- or halogen-substituted derivatives thereof as well as esterforming derivatives such as ester derivatives and acyl halide thereof.

According to the present invention, the molar proportions of eachrepeating units of formula [III] and formula [IV] based on the totalamount of the repeating units of formulae [I]-[IV], i.e., r and s, are2-15, and preferably 5-13. In addition, in the liquid-crystallinepolyester resin of the present invention, it is preferable that themolar amounts of the repeating units of formula [III] and those of therepeating units of formula [IV] are substantially equal, i.e., r=s.

The method for preparing the liquid-crystalline polyester resin of thepresent invention is not limited and any known method can be employed.For example, conventional polymerization methods such as moltenacidolysis method and slurry polymerization method for preparingpolyester to give ester bondings among the above described monomercomponents may be employed.

The molten acidolysis method is preferably used for the presentinvention. In this method, the polymerizing monomers are heated to givea molten solution of the reactants and then the solution is reacted togive the molten polymer. The final step of this method may be carriedout under vacuum to facilitate the removal of the volatile by-productssuch as acetic acid or water.

The slurry polymerization method is characterized in that monomers arereacted in a heat exchange fluid to give the solid state polymer in theform of suspension in the heat exchange liquid medium.

In either of the molten acidolysis method or the slurry polymerizationmethod, the polymerizing monomer components used for the preparation ofthe liquid-crystalline polyester resin may be in the denatured form,i.e. in the form of C₂-₅ acyl esters, which are obtained by esterifyingthe hydroxyl groups. Among the C₂-₅ acyl groups, C₂-₃ acyl groups arepreferable. Acetic esters are most preferably used for the reaction.

The C₂-₅ acyl esters of the monomers may be those prepared beforehand byacylating the monomers independently or may be those produced in thereaction system by adding an acylating agent such as acetic anhydride tothe monomers upon preparing the liquid-crystalline polyester.

In either of the molten acidolysis method or the slurry polymerizationmethod, a catalyst may be used in the reaction, if desired.

Examples of the catalysts include organic tin compounds such as dialkyltin oxide (ex. dibutyl tin oxide) and diaryl tin oxide; organic titaniumcompounds such as titanium dioxide, antimony trioxide, alkoxy titaniumsilicate and titanium alkoxide; alkaline or alkaline earth metal salt ofcarboxylic acid such as potassium acetate; alkaline or alkaline earthmetal salt of inorganic acid such as potassium sulfate and gaseous acidcatalysts such as Lewis acid (ex. BF₃) and halogenated hydrogen (ex.HCl).

When a catalyst is used, the amount of the catalyst added to thereaction based on the total monomers may preferably be 10-1000 ppm, andmore preferably 20-200 ppm.

The melting point of the liquid-crystalline polyester resin of thepresent invention determined using differential scanning calorimeter(DSC) according to the method described below is 190-250° C., preferably200-240° C., and more preferably 210-230° C. The liquid-crystallinepolyester resin of the present invention with such a low melting pointexhibits a good molding processability at low temperatures.

<Method for Determining the Melting Point with DSC>

The differential scanning calorimeter Exstar 6000 (Seiko InstrumentsInc., Chiba, Japan) or the same type of DSC device is used. The LCPsample to be examined is heated from room temperature at a rate of 20°C./minute and endothermic peak (Tml) is recorded. Thereafter, LCP sampleis kept at a temperature 20-50° C. higher than Tml for 10 minutes. Thenthe sample is cooled to room temperature at the rate of 20° C./minute.Then, LCP sample is heated again at the rate of 20° C./minute andexothermic peak is recorded. Endothermic peak found in the final step isrecorded as melting point.

Preferably, the liquid-crystalline polyester resin of the presentinvention is that log viscosity of the same can be measured inpentafluorophenol. The log viscosity of the polymer measured at aconcentration of 0.1 g/dl in pentafluorophenol at 60° C. may preferablybe 0.3 dl/g or above, more preferably 0.5-10 dl/g, and most preferably1-8 dl/g.

The melting viscosity of the liquid-crystalline polyester resin of thepresent invention measured with capillary rheometer may preferably be1-1000 Pa·s, more preferably 5-300 Pa·s.

The present invention further provides a liquid-crystalline polyesterresin composition comprising the above-described liquid-crystallinepolyester resin. The liquid-crystalline polyester resin composition maybe those obtained by admixing one or more fibrous, plate or particulatefiller and/or reinforcement to the liquid-crystalline polyester resin.

The filler and/or reinforcement may be selected from any of conventionalreinforcements and/or fillers for resin compositions depending on theintended use and application of the liquid-crystalline polyester resincomposition.

Examples of fibrous fillers and/or reinforcements may include glassfiber, silica-alumina fiber, alumina fiber, carbon fiber and aramidfiber. Among them, glass fiber is preferably used.

Examples of plate or particulate fillers and/or reinforcements mayinclude talc, mica, graphite, wollastonite, calcium carbonate, dolomite,clay, glass flake, glass beads, barium sulfate and titanium oxide.

The fillers and/or reinforcements may be added to the liquid-crystallinepolyester resin composition in an amount of 0.1-200 parts by weight,especially 10-100 parts by weight to 100 parts by weight of theliquid-crystalline polyester resin.

The liquid-crystalline polyester resin of the present invention whichdoes not contain any additional component other than theliquid-crystalline polyester resin, such as the LCP including no fillerand/or reinforcement and the like may be suitably used.

If the amount of fillers and/or reinforcements is more than 200 parts byweight, the moldability of the resulting liquid-crystalline polyesterresin composition tends to be decreased or the exhausting of thecylinder or die of the molding device tends to be increased.

The liquid-crystalline polyester resin composition according to thepresent invention may further be admixed with one or more additivesconventionally used for resin compositions, if desired, for examplemolding lubricant such as higher aliphatic acid, higher aliphatic ester,higher aliphatic amide, higher aliphatic acid metal salt, polysiloxaneand fluorocarbon resin; colorant such as dyes and pigments; antioxidant;thermal stabilizer; UV absorbent; antistatic agent and surface activeagent.

The amount of additives admixed is not limited and may be selecteddepending on the intended use or purpose of the liquid-crystallinepolyester resin composition. Typically, additives may be added to theliquid-crystalline polyester resin composition of the present inventionin an amount of 0.005-1.0 parts by weight, preferably 0.01-0.5 parts byweight per 100 parts by weight of the liquid-crystalline polyesterresin. The term “higher” group herein used refers to the group of 10-25carbon atoms.

Molding lubricants such as higher aliphatic acid, higher aliphaticester, higher aliphatic acid metal salt or fluorocarbon-type surfactantmay be added to the pellets of the liquid-crystalline polyester resin orthe liquid-crystalline polyester resin composition before subjecting thepellets to the molding process, so that the agent adhere to the outersurface of the pellets.

The liquid-crystalline polyester resin composition of the presentinvention may comprise one or more additional resin component unless theadditional resin component does not impair the object of the presentinvention. Examples of the additional resin components includethermoplastic resins such as polyamide, polyester, polyphenylenesulfide, polyether ketone, polycarbonate, polyphenylene ether anddenatured derivatives thereof, polysulfone, polyethersulfone andpolyether imide and thermosetting resins such as phenol resin, epoxyresin and polyimide resin. The amount of the additional resin componentis not limited, and may be determined dependent on the intended use andapplication. Typically, such additional resins may be added to theliquid-crystalline polyester resin composition in an amount of 0.1-200parts by weight, preferably 10-100 parts by weight per 100 parts byweight of the liquid-crystalline polyester resin.

The liquid-crystalline polyester resin composition of the presentinvention may be obtained by adding fillers, reinforcements and otherresin components to the polyester resin and melt kneading the mixture ata temperature from near the melting point of the polymer to the meltingpoint plus 100° C. using a kneading machine such as Banbury mixer,kneader, single screw extruder, twin screw extruder or the like.

The liquid-crystalline polyester resin and the liquid-crystallinepolyester resin composition according to the present invention may bemolded into a molded article with a desired shape by using aconventional melt molding process, preferably injection molding,compression molding, extrusion molding and blow molding.

BRIEF DESCRIPTION OF DRAWING

FIG. 1 shows the relationship of molar ratios of BON6/POB and meltingpoints of the liquid-crystalline polyester resins obtained by Examples4-6 and Comparative examples 1-2.

EXAMPLES

The present invention is further described in reference to the followingexamples. The following examples are intended to illustrate theinvention and are not to be construed to limit the scope of theinvention.

In the examples and the drawing, following abbreviations are used.

-   BON6: 6-hydroxy-2-naphthoic acid-   POB: p-hydroxybenzoic acid-   HQ: hydroquinone-   BP: 4,4′-dihydroxybiphenyl-   TPA: terephthalic acid-   NDA: 2,6-naphthalenedicarboxylic acid

Example 1

BON6, POB, HQ and TPA of which the proportions are shown in Table 1below were fed in a reaction container equipped with an agitating devicewith torque-meter and a condenser so that the total monomer amount was 5moles. Then 0.05 g of potassium acetate and acetic anhydride of 1.025fold moles to the total amount of hydroxyl groups of the monomers wereadded to the container. The polymerizing reaction was conductedaccording to the procedure described below. TABLE 1 Example 1: monomerproportions BON6 POB HQ TPA g 386 297 44 67 (mol %) 41 43 8 8

Under the nitrogen atmosphere, the mixture was heated from roomtemperature to 150° C. over one hour and kept at the temperature for 30minutes, then rapidly heated to 210° C. with distilling out theby-product acetic acid and kept at the temperature for 30 minutes. Thenthe mixture was heated to 335° C. over 3 hours and the pressure wasreduced to 20 mmHg over 30 minutes. When the torque became thepredetermined level, the polymerizing reaction was terminated. Theresulting resin was removed from the container and crushed with crusherto give pellets of the liquid-crystalline polyester resin. As a result,the approximately theoretical amount of acetic acid was distilled out.The melting point of the resulting liquid-crystalline polyester resindetermined by DSC was 221° C.

Example 2

Pellets of the liquid-crystalline polyester resin were obtainedaccording to the same manner as described in Example 1 with theexception that the monomer proportions were changed to those shown inTable 2 below. As a result, the approximately theoretical amount ofacetic acid was distilled out. The melting point of the resultingliquid-crystalline polyester resin determined by DSC was 210° C. TABLE 2Example 2: monomer proportions BON6 POB BP NDA g 377 277 93 108 (mol %)40 40 10 10

Example 3

Pellets of the liquid-crystalline polyester resin were obtainedaccording to the same manner as described in Example 1 with theexception that the monomer proportions were changed to those shown inTable 3 below. As a result, the approximately theoretical amount ofacetic acid was distilled out. The melting point of the resultingliquid-crystalline polyester resin determined by DSC was 218° C. TABLE 3Example 3: monomer proportions BON6 POB HQ BP NDA g 377 318 22 28 76(mol %) 40 46 4 3 7

Example 4

Pellets of the liquid-crystalline polyester resin were obtainedaccording to the same manner as described in Example 1 with theexception that the monomer proportions were changed to those shown inTable 4 below. As a result, the approximately theoretical amount ofacetic acid was distilled out. The melting point of the resultingliquid-crystalline polyester resin determined by DSC was 218° C. TABLE 4Example 4: monomer proportions BON6 POB HQ TPA g 377 277 55 83 (mol %)40 40 10 10

Example 5

Pellets of the liquid-crystalline polyester resin were obtainedaccording to the same manner as described in Example 1 with theexception that the monomer proportions were changed to those shown inTable 5 below. As a result, the approximately theoretical amount ofacetic acid was distilled out. The melting point of the resultingliquid-crystalline polyester resin determined by DSC was 228° C. TABLE 5Example 5: monomer proportions BON6 POB HQ TPA g 480 200 55 83 (mol %)51 29 10 10

Example 6

Pellets of the liquid-crystalline polyester resin were obtainedaccording to the same manner as described in Example 1 with theexception that the monomer proportions were changed to those shown inTable 6 below. As a result, the approximately theoretical amount ofacetic acid was distilled out. The melting point of the resultingliquid-crystalline polyester resin determined by DSC was 230° C. TABLE 6Example 6: monomer proportions BON6 POB HQ TPA g 273 352 55 83 (mol %)29 51 10 10

Comparative Example 1

Pellets of the liquid-crystalline polyester resin were obtainedaccording to the same manner as described in Example 1 with theexception that the monomer proportions were changed to those shown inTable 7 below. As a result, the approximately theoretical amount ofacetic acid was distilled out. The melting point of the resultingliquid-crystalline polyester resin determined by DSC was 255° C. TABLE 7Comparative example 1: monomer proportions BON6 POB HQ TPA g 188 415 5583 (mol %) 20 60 10 10

Comparative Example 2

Pellets of the liquid-crystalline polyester resin were obtainedaccording to the same manner as described in Example 1 with theexception that the monomer proportions were changed to those shown inTable 8 below. As a result, the approximately theoretical amount ofacetic acid was distilled out. The melting point of the resultingliquid-crystalline polyester resin determined by DSC was 253° C. TABLE 8Comparative example 2: monomer proportions BON6 POB HQ TPA g 518 173 5583 (mol %) 55 25 10 10

In Examples 4-6 and Comparative examples 1-2, proportions of HQ and TPA,which provide repeating units of formulae [III] and [IV] respectively,were kept constant at 10 mol % and those of BON6 and POB, which providerepeating units of formulae [I] and [II], were changed. FIG. 1 shows therelationship of the molar ratios of BON6/POB, i.e., p/q, and the meltingpoints of the resulting liquid-crystalline polyester resins.

INDUSTRIAL APPLICABILITY

The liquid-crystalline polyester resin and the liquid-crystallinepolyester resin composition of the present invention are useful forparts of electric and electronic devices, machines and automobiles. Inparticular, the liquid-crystalline polyester resin of the presentinvention is suitably used for the applications which require goodprocessability at low temperatures.

1. A liquid-crystalline polyester resin, essentially consisting of therepeating units represented by formulae [I]-[IV]:

wherein Ar₁ and Ar₂ independently represent one or more bivalentaromatic group; p, q, r and s represent relative molar proportions (mol%) of the repeating units based on the total repeating units representedby formulae [I]-[IV] in the liquid-crystalline polyester resin andsatisfy the following formulae:0.4≦p/q≦2.0,2≦r≦15,2≦s≦15, andp+q+r+s=100, provided that the liquid-crystalline polyester resin has amelting point of 190-205° C. determined by differential scanningcalorimetry.
 2. The liquid-crystalline polyester resin according toclaim 1, wherein p, q, r and s satisfy the following formulae:35≦p≦48,35≦q≦48,2≦r≦15,2≦s≦15, andp+q+r+s=100.
 3. The liquid-crystalline polyester resin according toclaim 1, wherein: Ar₁ represents:

Ar₂ represents:


4. The liquid-crystalline polyester resin according to claim 1, whereinboth Ar₁ and Ar₂ represent:


5. A liquid-crystalline polyester resin composition comprising 100 partsby weight of the liquid-crystalline polyester resin according to claim 1and 0.1-200 parts by weight of one or more of fibrous, plate orparticulate filler and/or reinforcement.
 6. A molded article obtained bymolding the liquid-crystalline polyester resin or the liquid-crystallinepolyester resin composition according to claim
 1. 7. Theliquid-crystalline polyester resin according to claim 2, wherein: Ar₁represents:

Ar₂ represents:


8. The liquid-crystalline polyester resin according to claim 2, whereinboth Ar₁ and Ar₂ represent: